JPS5810131Y2 - Sulfur dioxide fluorescence detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas sampling device, and more particularly to a device for detecting and quantizing the amount of sulfur dioxide in a gas sample by means of fluorescence technology.

Sulfur dioxide is one of the major air pollutants in ambient air.

In the past, it has been desirable, and in many cases required by law, to monitor the amount of sulfur dioxide contained in the ambient air or in gas streams discharged into the ambient air.

Currently, sulfur dioxide SO2 is monitored by one of the following methods.

(2) Wet chemical coulometric technology, commonly known as the West-Gaeke method.

2. Electroanalysis technology.

3. H2 flame flashing technology.

4. Gas-phase spectrometry, optical technology, including ultraviolet UV and Akai line I, R, absorption and U, V, fluorescence.

Of these methods, WeSt-Gaeke and electroanalytical methods are slow to respond and are not suitable for long periods of unmaintained operation.

In the case of flame photometry, there is also a response to other sulfur compounds that is not linear with respect to the signal output SO2 concentration and at various sensitivities.

U, V, and I, R absorption techniques are not sensitive enough to monitor ppm levels.

U, V, fluorescence technology is the most promising as it does not have the above drawbacks.

Sulfur dioxide is known to fluoresce when excited by light of appropriate wavelengths in the ultraviolet region of the electromagnetic spectrum.

Recently, the use of U, V, fluorescence has become popular as a means of monitoring ambient sulfur dioxide.

A typical fluorescence analyzer is 225. narrowband U, V centered at Onm and having a bandwidth of 25.9 nm;
A light source, a lens that parallelizes the light, a suitable interference filter,
Sample fluorescence flow cell, optical trap, detection filter,
It consists of a sensitive photomultiplier tube, a pump, a pressure regulation system, and a flow control and/or monitoring system.

The operation of this device will be described below in connection with the preferred embodiment of the invention.

To illustrate the basic principle of operation, the sample gas to be analyzed is introduced into a fluorescent flow cell and irradiated with ultraviolet light consisting of said narrow band of wavelengths selected to cause fluorescence in the SO2 gas contained in the sample. The generated fluorescence of SO2 is detected and quantized by a photomultiplier tube and associated electronics.

Xenon, zinc and cadmium lamps have been used as light sources to isolate the desired wavelengths.

More desirable wavelengths were obtained from zinc lamps.

Instruments so designed by the researchers, and at least one commercially available product, have apparently performed satisfactorily when tested on certain syngas blends, and are also claimed to be valid on ambient air.

However, research conducted by the inventor on such devices has shown that there is significant interference from other gases.

When tested individually, about 15 types of gas (No.
(including CO and several hydrocarbons) did not show a significant effect on the output data in the detection of U, V, and SO2.

However, the ambient air containing a large number of potential interfering substances
When monitored simultaneously with an O2 fluorescence analyzer and a coulometric SO2 analyzer (high precision), the fluorescence analyzer gave significantly different data than the coulometric analyzer.

Therefore, despite claims to the contrary, SO2
Fluorescent monitoring technology requires improvements beyond the current state of the art to be practical for monitoring ambient SO2.

It is therefore an object of the present invention to provide an improvement in a SO2 detection device using ultraviolet excitation and detection of emitted fluorescence, in order to overcome the aforementioned disturbing drawbacks and to enable reliable measurements. It is.

This objective is achieved by incorporating a reactor into the sample stream in front of the photodetector.

In one embodiment using ozone in the reactor, a dryer is added before the reactor.

The dryer removes moisture from the incoming sample stream and prevents the formation of H2SO4 which would cause undesirable errors in subsequent reactors.

The reactor is heated with oxidizing agents, such as heated pure carbon, heated quartz, etc.
Alternatively, use a broadband U, V, light source that can generate ozone from oxygen in the sample stream.

The reactor in each case has an oxidizing effect on the molecules of the interfering substance, so that the interfering substance is converted into a non-fluorescent substance.

During the development of the SO2 fluorescence analyzer, samples were taken from the prototype and coulometric analyzers, specifically the Beckman model 906A, in order to determine the accuracy and precision of the results obtained with the Pro 1 to type fluorescence analyzers.
The SO2 analyzer was fed simultaneously (from the same manifold).

The two instruments were exposed to clean calibration samples (wet and dry) obtained by passing clean air through a SO2 infiltration tube or by taking a compressed mixture of SO2 and clean air directly from a steel cylinder.

Since the coulometric analyzer was the main instrument, no span adjustment was required and its reading was taken as the standard.

The optical analyzer was adjusted accordingly.

When calibrated at one value (approximately lppm), the two analyzers range from 5ppb to 2000 ppb (2ppm)
(7) Tracking within the concentration range ±1%
ck) I did.

However, when the two analyzers were exposed to ambient samples, the responses were widely dispersed.

Typically 5-50 as measured with a coulometric analyzer
For ambient SO2 in the ppb range, the fluorescence analyzer showed a response up to 250 ppb (under worst-case conditions) above that indicated by the coulometric analyzer, depending on the ambient composition of the minor contaminant. Dew.

The ambient air contained varying amounts of ozone, nitrogen oxides, and various hydrocarbons.

Conditions were also found to vary according to time of day.

The worst ambient conditions typically occurred between 8-10 a.m. and 4-6 p.m.

Because of these worst-case conditions and the associated environment, it was assumed that the main contaminants were hydrocarbons, especially polynuclear aromatic hydrocarbons.

The interfering components are acenaphthene, acenaphthylene, anthracene, benz1a]anthracene-7,12-dione,
It is believed to include benzo, (ghi]perylene, ri)cene, coronene, dibenzofuran, dibenzothiophene, fluoranthrene, naphthalene, perylene, phenanthrene and pyrene.

One of the inventors of the present invention was also a co-inventor of a reactor capable of removing hydrocarbons as interfering substances in a sample gas stream.

This reactor is assigned to the assignee of the present invention, R.M.
, Neti and R.L., Roggenkamp, US Pat. No. 4,063,895.

Therefore, the possibility of using this reactor with a fluorescent SO2 analyzer was investigated.

In order to match the response of the fluorescence analyzer using the sample described above to that of the coulometric analyzer (25
01) ±5 ppb or less in pb full scale range), sample (yes only through optical analyzer)
are 184.9, 253.7, 303.6 and 403
．． Conditioned by passing through a reactor consisting of an enclosure containing a high purity quartz lamp producing ultraviolet radiation in the 6 nm band.

The action of this broadband U, V, ray, i.e. the ozone generated by the lamp from the oxygen in the passing air, is to oxidize the interfering substances, and this agreement between the responses of the fluorescent and coulometric analyzers is obtained. Ta.

However, it was found that the above agreement between the responses of the fluorescence analyzer and the coulometric analyzer where the sample gas passes through the U, V, oxidation reactor is obtained only in the case of dry samples (ambient and synthetic). It was done.

Water vapor was not an interfering substance before U, V, and radiation were introduced, but after U, V, and irradiation, including the 184.9 nm line, water vapor had a strong quenching effect on the SO2 response in the fluorescence analyzer. was discovered.

When water vapor was added to a sample containing SO2, the fluorescence analyzer showed up to about 90% attenuation, while the coulometric analyzer only showed up to 10% power loss.

These experiments showed that U in the reactor where water vapor is present,
V, in the irradiation process, SO2 becomes SO3 and possibly H
It was suggested that it was oxidized to 2SO4, resulting in a loss of signal from the preparation sample.

This quenching effect due to the presence of water vapor in the U, V, and preparation samples was of course undesirable.

Quenching was decapitated by drying the sample through a commercially available high quality dryer before passing through the U, V reactor.

The dryer had to be able to remove water vapor without attenuating the SO2 response.

Oceanport, New Chassis
rt) of Perma Pure Produc Co., Ltd. (Perma
Permeation dryer manufactured by Pure Products, Inc.
Box (7) was found to be suitable for the purpose.

Simply put, this dryer uses a water vapor permeable membrane,
A water vapor-containing sample gas and a dry purge gas flow in a countercurrent relationship with this membrane as a boundary, and the dry gas sucks out water vapor in the sample gas through the membrane and carries it away.

In an apparatus in which the sample gas was first dried in an oven and then irradiated with U, V, generated by a quartz lamp, the ambient sample monitored simultaneously by the coulometric and fluorescence analyzers had a full scale concentration of 250 ppb. showed a consistent response within ±5 ppb 302 in the range of .

These results were found to be true for all possible moderate ambient conditions investigated.

As an example of an unsuitable condition, if the fluorescence analyzer intake is placed facing the exhaust gases within two feet of the exhaust pipe of an automobile, the interfering substances are the dryer and the quartz lamp U,
Although it was significantly reduced by the combination of V and irradiation, it could not be completely eliminated.

A first embodiment of the device of the invention is shown in FIG.

Sample gas 10 is introduced through intake port 12 . Intake port 12
The sample gas passes through the particle filter 14 and the sample gas 1
Particulate matter is removed from 0.

The sample gas 10 then passes through a dryer 16 connected to a filter 14.

Ideally, the dryer 16 should be capable of removing substantially all moisture from the sample gas 10 without affecting the SO2 content of the sample gas 10.

The osmotic dryer described above is preferred in this embodiment.

The output of the dryer 16 is connected to a U, V reactor 18, which makes it possible to eliminate the influence of interfering substances in the sample gas 10 by means of an oxidizing action.

The reactor 18 is arranged to irradiate the sample gas passing therethrough with a broad range of wavelengths, including the 184.9 nm line (which generates ozone from the oxygen in the sample gas 10) and the 253.7 nm line. , V light.

The output of oxidation reactor 18 is connected to the input of optical analyzer 20.

Fluorescence analyzer 20 includes a fluorescence plug 22 into which sample gas 10 is introduced.

The ultraviolet irradiation source 24 directs narrow band collimated ultraviolet light centered at approximately 225.0 nm into the pilot vehicle 22, where the ultraviolet light irradiates the sample gas 10 and removes SO2 in the sample gas.
It emits light.

This SO2 fluorescence is detected by a photomultiplier tube 26.

The photomultiplier tube 26 is connected via suitable electronic circuitry 28 to a display device 30 which indicates the SO2 content of the sample gas 10 in a form understandable to the operator.

The output of the fluorescence analyzer 20 is the ozone scrubber 3.
2, this scrubber removes ozone generated in the reactor 20 from the oxygen in the sample gas 10 and remaining in the sample stream.

Ozone should be removed to prevent damage to components within the backpressure regulator and pump contained in the downstream portion of the equipment.

A flow meter 34 is connected to the output of the ozone scrubber 32 and a capillary tube 36 is connected to the output of the flow meter 34.

The pressure gauge 38 includes an ozone scrubber 32 and a flow meter 34.
Connected to the connection between.

The system between the inlet 12 and the capillary tube 36 is therefore intended to operate at atmospheric pressure and constant flow, so that the detection of SO2 is pressure independent.

The pressure gauge 38 makes it possible to monitor the pressure in the pilot vehicle 22, which may change due to, for example, a blockage of the filter 14.

A back pressure regulator 40 for maintaining a constant flow rate is a capillary tube 36.
connected to the output of

Pressure regulator 40 bootstraps dryer 16.
otstrap) section or the entrance of the self-help section.

The dryer 16 facilitates the drying process of the vacuum sample in a manner characteristic of an osmotic dryer using semi-permeable membranes that are particularly suited for this application.

The outlet of the bootstrap portion of the dryer 16 is connected to the pump 42.
This pump is used to generate a partial vacuum to draw sample gas 10 through fluorescence analyzer 20 and to aid in the drying process.

The outlet of pump 42 is connected to exhaust outlet 44 .

The flow rate within the device is not critical.

It has been found that about 1000-1500 cc/min is a suitable flow rate.

If the flow rate is too high, the interfering substances will not have time to be completely removed by the reactor.

Although the devices described above are suitable for their intended purpose, the increased cost of using a dryer and ozone scrubber penalizes the commercialization of such devices.

Therefore, another device was sought that could oxidize interfering substances without the need for a dryer and an ozone scrubber.

In the pursuit of such viable alternative devices, the various reactors used in Applicant's instrumentation have been tested for their adaptability for use as oxidizers for hydrocarbons in sample gases, including SO2. was investigated.

One such reactor is described in R,M, Netino US Pat. No. 3,870,468.

This patent discloses the conversion of nitrogen dioxide to nitric oxide for subsequent detection by chemiluminescence technology.

That is, nitrogen dioxide is passed through a limited volume reactor where concentrated heat is applied in the presence of vitreous carbon.

It has been found that when a sample gas containing interfering hydrocarbons is passed through such a reactor, the hydrocarbons are substantially completely oxidized, while the SO2 contained in the sample gas is not substantially affected. It was done.

Although other means of oxidizing hydrocarbons in the sample stream have been found without affecting the SO2 content, the glassy carbon reactor became the preferred embodiment at the time of this application.

The reactor according to said patent consists of a restricted channel through which the sample gas is passed.

300-600℃, preferably about 450℃ within this restricted path.
Contains substantially pure carbon that has been heated to .

The carbon used in the test equipment was manufactured by Garland, Texas.
arland)'s POCOG
raphite, Inc.) and California Well 1, Van Nuys (7) Beckwith, Corp.
It was obtained from.

The former product is called Poco Graphite, and the latter product is called Glassy Carbon.

In describing nitrogen dioxide conversion, the patent suggests pellets or rods of vitreous carbon.

In the present invention, excellent results were obtained using Poco Graphite X 4029 (fine pellets), which is completely transparent to SO2.

Although not specifically tested, prior experience concludes that soft, high purity carbon can be used at significantly lower temperatures.

Of course, such reactors must be refilled from time to time as the carbon is consumed, and in this respect they differ from hard glassy carbon reactors.

Experience also suggests that so-called activated carbon must be avoided.

The reason is that activated carbon also tends to capture and extract SO2.

A preferred embodiment of the device of the present invention is shown in FIG.

Corresponding elements are designated with the same reference numerals as in FIG. 1 and have the same functions.

In this case, the dryer 16 and ozone scrubber 32 are not needed and are therefore eliminated.

Glassy carbon reactor 18' is used in place of U, V reactor 18, but performs the same function of oxidizing the hydrocarbons in sample gas 10.

Although the reactor 18' is placed in front of the particle filter 14, this is only an option.

That is, filter 14 is an optional feature (along with pressure gauge 38 and flow meter 34) that was preferably included to provide superior performance to commercially available instruments.

Although ultra-high purity carbon in the presence of ozonation U, V and heat has previously been described in detail as a suitable means of oxidizing hydrocarbons in sample gas streams without affecting the SO2 content, additional Measures have been considered and tested in many cases.

A number of approaches are promising enough to be considered as direct substitutes, such as the hydrocarbon oxidation reactor 18' of the SO2 detection system of FIG.

These include quartz heated to a temperature above 700°C, preferably 900°C, and stainless steel heated to about 400°C.

However, when heated stainless steel is used, S
There was some loss of O2.

Additionally, platinum black or palladium maintained at ambient temperature to 200°C was able to oxidize hydrocarbons, but was moisture sensitive.

Therefore, in order to use these, a dryer is required as shown in FIG. 1, but an ozone scrubber is not necessary.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the components of an embodiment of the sulfur dioxide detection device of the present invention. FIG. 2 is a block diagram of the components of a preferred embodiment of the sulfur dioxide detection device of the present invention. 10... Sample gas, 12... Intake port,
14... Filter, 16... Dryer, 18... Reactor, 20... Fluorescence analyzer, 22... Fluorescence filling, 24...
・・UV source, 26・・Photomultiplier tube, 28・
...Electronic circuit, 30...Display device, 32...Ozone scrubber, 34...
...Flowmeter, 36...Capillary, 38...
...Pressure gauge, 40...Back pressure regulator, 42.
...Pump, 44...Exhaust outlet.

Claims (1)

[Claims for Utility Model Registration] (i) a fluorescent chamber adapted to hold a gas sample; a source of narrow-band ultraviolet light arranged to irradiate the gas sample within said fluorescent chamber; and said narrow-band ultraviolet light; detecting sulfur dioxide in an ambient gas sample, including a photomultiplier tube positioned to determine the amount of sulfur dioxide in the gas sample by measuring the level of fluorescence in the gas sample when irradiated by the an apparatus for oxidizing hydrocarbons in a gas sample to eliminate the error-generating reaction during subsequent analysis of the gas sample, the oxidizer being connected to an input for receiving the gas sample and to a fluorescence chamber; The sulfur dioxide detection device is characterized in that it has an output of: 2. The oxidizer converts high-purity carbon and the carbon to 300~
2. A sulfur dioxide detection device according to claim 1, comprising a device for heating to a temperature in the range of 600°C. 3. The sulfur dioxide detection device of claim 2, wherein the heating device is adapted to maintain the carbon at a temperature of about 400°C. 4. The sulfur dioxide detection device according to item 1, wherein the oxidizing device includes quartz and a device for heating the quartz to a temperature higher than 700°C. 5. The sulfur dioxide detection device of claim 4, wherein the heating device is adapted to maintain the quartz at a temperature of about 900°C. 6. The sulfur dioxide detection device according to claim 1, wherein the oxidizing device includes stainless steel and a device for heating the stainless steel to about 400°C.